System and method for controlling four-quadrant operation of a switched reluctance motor drive through a single controllable switch

ABSTRACT

A single controllable switch ( 509 ) drive system for regulating the speed of a two-phase switched reluctance machine (TPSRM) ( 700 ) rotor may include a speed control feedback loop ( 970 ) component that uses an established speed control signal and a signal indicative of the rotor&#39;s speed to dynamically adjust a first parameter. And a current control feedback loop ( 976 ) component that uses an established current control signal and a signal indicative of the current flowing through a stator winding ( 505,508 ) of the TPSRM to dynamically adjust a second parameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.60/614,547 and incorporates by reference this provisional application inits entirety. Additionally, the application incorporates by referencethe disclosures provided in Applicant's co-pending PCT InternationalApplication Nos. PCT/US03/16627, PCT/US03/16628, PCT/US03/16629,PCT/US03/16630, and PCT/US03/16631.

FIELD OF THE INVENTION

The present invention relates to a method and system for controlling theoperation of a two-phase switched reluctance machine (TPSRM). Morespecifically, the invention relates to controlling the TPSRM with apower converter employing a single controllable switch.

BACKGROUND OF THE RELATED ART

A two-phase switched reluctance machine (TPSRM) is a switched reluctancemachine (SRM) with two phases, phases A and B. displaced from each otherby 180 degrees/n, where n is the number of stator poles per phase. FIGS.7( a) and 7(b) illustrate a two-phase SRM 700 of the related art. TPSRM700 has four stator poles 9-12 and two rotor poles 13, 14 and ischaracterized as a two-phase machine with a 4/2 stator/rotor polecombination (i.e., 4 stator poles and 2 rotor poles). The rotor rotatesabout a rotor shaft 15.

FIG. 7( a) illustrates TPSRM 700 and its flux paths through back ironsegments 1-8, stator poles 9, 11, and rotor poles 13, 14 during theexcitation of phase A. FIG. 7( b) illustrates TPSRM 700 and its fluxpaths through back iron segments 1-8, stator poles 10, 12, and rotorpoles 13, 14 during the excitation of phase B. The phase A excitation isinduced by winding 16, 16′ around stator pole 9 and another winding 17,17′ on the diametrically opposed stator pole 11. Winding 16, 161 andwinding 17, 17′ may be connected in series or in parallel. The phase Bexcitation is induced by winding 18, 18′ around stator pole 10 andanother winding 19, 19′ on the diametrically opposed stator pole 12.Winding 18, 18′ and winding 19, 19′ may similarly be connected in seriesor in parallel. In each of FIGS. 7( a) and 7(b), the rotor poles arepositioned in alignment with the stator poles whose windings are beingenergized.

Excitation of the phase B windings is initiated when rotor pole 14 ispositioned between stator poles 9 and 10 and rotor pole 13 is positionedbetween stator poles 11 and 12. The rate of change of inductance will bepositive in this region and, hence, positive torque will be produced. Asa result, rotor poles 14 and 13 will rotate clockwise (CW) toward thephase B stator poles 10 and 12, respectively. When rotor poles 14 and 13pass around phase B stator poles 10 and 12, respectively, the phase Awindings will be excited, causing rotor poles 14 and 13 to rotate CWtoward the phase stator poles 11 and 9, respectively.

To reverse the direction of rotation, phase B windings 18, 18′ and 19,19′ are excited when rotor pole 14 is between stator poles 12 and 9 androtor pole 13 is between stator poles 10 and 11. If the rotor poles arecloser to phase B stator poles 10 and 12, the rotor will rotate towardthem resulting in counter-clockwise (CCW) rotation. Therefore,controlling the rotor's direction of rotation involves the independentcontrol of the phase A and B excitations. If such independent control ofindividual phase excitation is not possible, there is no control methodthat can reverse the machine's rotor rotation from one direction toanother.

Related art TPSRMs are driven by two or four controllable switch-basedpower converters. Some examples are described below.

FIG. 1 illustrates a related art asymmetric power converter 100 fordriving a two-phase SRM. Power converter 100 has two controllableand-two uncontrollable power devices for each phase winding 101, 102 ofthe SRM. Therefore, four controllable 103-106 and four uncontrollable107-110 power devices are required for power converter 100 to operate.The primary advantage of power converter 100 is that it gives fullcontrollability in terms of its ability to apply full positive ornegative direct current (dc) link voltage, and, therefore, it does notdiminish or restrict any operating mode of the SRM. The disadvantage ofthis power converter topology is that it uses eight power devices. Amore detailed description of power converter 100's circuit operation maybe found in “Switched Reluctance Motor Drives”, R. Krishnan, CRC Press,June 2001.

FIG. 2 illustrates a related art single switch-per-phase power converter200 for driving a two-phase SRM. Power converter 200's circuit topologyis based on splitting a dc input source voltage 201 equally to themachine side power converter. This results in a circuit requiring onecontrollable and one uncontrollable power device per phase winding 202,203. Therefore, overall, power converter 200 requires two controllablepower devices 204, 205 and two uncontrollable power devices 206, 207 fora two-phase SRM. The major advantage of this circuit design is that ituses a reduced number of power devices (e.g., a total of four) comparedto the asymmetric converter. The disadvantage of this circuit is that itreduces the available dc source voltage by half and, therefore, doublesthe current rating required for the devices and for the machine,resulting in low efficiency machine operation. A fuller description ofthis circuit may be found in “Switched Reluctance Motor Drives”, R.Krishnan, CRC Press, June 2001.

Some variations of the single-switch-per-phase topologies are describedby Harris in U.S. Pat. No. 5,075,610, by Webster in U.S. Pat. No.5,864,477, and by Disser et al. in U.S. Pat. No. 5,900,712. Harrisdescribes a circuit with a single-switch-per-phase topology thatrequires more than one diode per phase and additionally requires morethan one dc link capacitor. Also, the commutating voltages to the phasewindings of Harris' power converter are always less than the source dcvoltage in this circuit. These are severe limitations.

Webster and Disser each describe a single-switch-per-phase topologyrequiring two capacitors for storing energy in the circuit. Moreover,these topologies do not provide for a common emitter connection of theswitches, thereby creating an isolation requirement for the gate drivecircuits and a higher cost for the additional components. As a result ofthe above-mention and other factors, these circuits are strongly limitedto low cost variable speed applications.

FIG. 3 illustrates a related art C-Dump power converter 300 for drivinga two-phase SRM. Power converter 300's circuit uses three controllablepower devices 301-303 and three uncontrollable diodes 304-306, resultingin the use of six power devices. This is an intermediate circuit betweenthose illustrated in FIGS. 1 and 2. The operating modes are somewhatrestricted for this circuit, since it can apply a full dc source voltage309 to machine windings 307, 308 only in the positive direction.Furthermore, this circuit requires an external inductor 310 or aresistor (not shown) to dissipate the energy stored in a C-dumpcapacitor 311. Use of external inductor 310 increases the cost, whereasthe use of the power resistor (not shown) will result in a lowerefficiency of the system and higher package volume, due to increasedthermal considerations. Therefore, this circuit is not ideal for usewith two-phase SRMs. A more detailed description of this circuit may befound in “Switched Reluctance Motor Drives”, R. Krishnan, CRC Press,June 2001 and in Miller et al., U.S. Pat. No. 4,684,867, dated Aug. 4,1987.

FIG. 4 illustrates a related art single switch-per-phase power converter400 for driving a two-phase SRM. Power converter 400 requires oneuncontrolled power device 401, 402 and one controlled power device 403,404 per phase 405, 406, and therefore, requires four power devices tofunction. Furthermore, power converter 400 requires a special winding inthe machine, known as a bifilar winding. This special winding increasesthe copper volume in the machine windings, resulting in increased costfor the machine. Additionally, power switches 403, 404 experience highervoltage stresses due to the leakage inductance between the windings ofeach respective phase. This leakage inductance can be minimized butcannot be eliminated in a practical machine. Therefore, this convertercircuit is not widely used, despite the fact that a full dc sourcevoltage 407 can be impressed on the machine with full controllability ofthe current. A more in depth description of this circuit may be found in“Switched Reluctance Motor Drives”, R. Krishnan, CRC Press, June 2001and in Miller, U.S. Pat. No. 4,500,824, dated Feb. 19, 1985.

All other heretofore known two-phase power converter circuit topologiesfall into one of the above-described categories, in terms of the totalnumber of power devices required for their operation. From theforegoing, it may be seen that a minimum of two controllable powerdevices are required for operating a related art two-phase SRM.

Generally speaking though, commercial power converters used to drive atwo-phase SRM usually have more than two controllable switches and morethan two diodes. Circuits requiring only two controllable switches andtwo diodes have the disadvantages of high power loss, low efficiency,and a bifilar winding in the machine, thereby reducing the power densityof the machine. Therefore, existing solutions are not attractive withregard to considerations of high efficiency operation, full range ofspeed control, compactness in the converter's packaging and, mostimportantly of all, the overall cost of the system.

A fundamental challenge in power converter development has been toreduce the number of power devices, both controllable anduncontrollable, to a level corresponding to that of a single-quadrantchopper drive, such as is commonly used in a dc motor drive or in auniversal motor drive. A description of these drives is provided in“Switched Reluctance Motor Drives”, R. Krishnan, CRC Press, June 2001.When the number of power devices has been reduced to this level, abrushless SRM drive becomes commercially competitive for variable speedapplications. Moreover, the brushless SRM has the superior advantage ofhigh efficiency, since there are no brushes and commutators in the SRM.Also, the brushless SRM is further endowed with high-speed operability,high reliability, maintenance-free operation, greater overloadcapability and, most of all, a cost advantage over the dc motor drive.

All reference material cited herein is hereby incorporated into thisdisclosure by reference.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the above-describedproblems and limitations of the related art.

Another object of the invention is to provide a method and system forcontrolling the speed of a two-phase switched reluctance machine (TPSRM)with a power converter having only one controllable switch.

Still another object of the invention is to provide speed control for aTPSRM, controlled by a power converter having only one controllableswitch, during the transition from clockwise to counter-clockwiserotation and vice versa when the TPSRM is operating as a generator.

A further object of the invention is to provide speed control for aTPSRM, controlled by a power converter having only one controllableswitch, so as to recover mechanical energy from the machine's inertiaand that of its load and convert this energy to electrical energy so asto achieve the effect of an electric brake.

A further object of the invention is to provide speed control for aTPSRM, controlled by a power converter having only one controllableswitch, so as to operate the TPSRM in all or a subset of itsfour-quadrant torgue-versus-speed modes of operation, which are forwardmotoring, forward regeneration, reverse motoring, and reverseregeneration.

These and other objects of the invention may be achieved in whole or inpart by a method of regulating the speed of a two-phase switchedreluctance machine (TPSRM) rotor. According to this method, a motoringmode or a braking mode of operation is selected for the TPSRM. The rotorspeed is regulated, when the motoring mode is selected, using a controlsignal cooperatively produced by a speed control feedback loop and acurrent control feedback loop. When the braking mode is selected, therotor speed is regulated using a control signal produced by the currentcontrol feedback loop without the cooperation of the speed controlfeedback loop. The speed control feedback loop uses an established speedcontrol signal and a signal indicative of the rotor's speed todynamically adjust a first parameter governing the control signal. Thecurrent control feedback loop uses an established current control signaland a signal indicative of the current flowing through a stator windingof the TPSRM to dynamically adjust a second parameter governing thecontrol signal. The braking mode of operation converts the TPSRM'smechanical energy into electrical energy to produce a braking effect onthe rotation of the rotor.

The objects of the invention may also be achieved in whole or in part bya drive system for regulating the speed of a two-phase switchedreluctance machine (TPSRM) rotor. The system includes a speed controlfeedback loop component that uses an established speed control signaland a signal indicative of the rotor's speed to dynamically adjust afirst parameter, and a current control feedback loop component that usesan established current control signal and a signal indicative of thecurrent flowing through a stator winding of the TPSRM to dynamicallyadjust a second parameter. A control signal for regulating the speed ofthe TPSRM rotor is produced in accordance with the first and secondparameters when the TPSRM is operated in a motoring mode, and thecontrol signal for regulating the speed of the TPSRM rotor is producedin accordance with the second parameter but not the first parameter whenthe TPSRM's braking mode is selected. The braking mode of operationconverts the TPSRM's mechanical energy into electrical energy to producea braking effect on the rotation of the rotor.

The objects of the invention may be further achieved in whole or in partby a method of reversing the rotational direction of a two-phaseswitched reluctance machine (TPSRM) rotor. According to this method, theflow of current through a single controllable current valve is regulatedto maintain a forward motoring mode of operation for the TPSRM. Then,the flow of current through the single controllable current valve isregulated to cause the TPSRM's mechanical energy to be converted intoelectrical energy so as to produce a braking effect on the rotation ofthe rotor. Thereafter, the flow of current through the singlecontrollable current valve is interrupted for a period of time. Afterthe period of time has expired, the flow of current through the singlecontrollable current valve is regulated to induce the TPSRM's rotor toreverse its direction of rotation.

The objects of the invention may be further achieved in whole or in partby a system for reversing the rotational direction of a two-phaseswitched reluctance machine (TPSRM) rotor. The system includes acontroller and a single controllable current valve that regulates, underthe control of the controller, the current flowing through the currentvalve so as to establish the rotational direction and speed of therotor. Together, the controller and the current valve cooperate tomaintain a forward motoring mode of operation for the TPSRM, when theTPSRM's rotor is to continue rotating in its current direction. Also,the controller and the current valve cooperate to cause the TPSRM'smechanical energy to be converted into electrical energy so as toproduce a braking effect on the rotation of the rotor, when a reversalin the rotor's direction of rotation is to be achieved. After the rotorhas been braked, the controller and the current valve cooperate tointerrupt the flow of current through the single controllable currentvalve for a period of time. Then the controller and the current valvecooperate to regulate the flow of current through the singlecontrollable current valve to induce the TPSRM's rotor to reverse itsdirection of rotation.

The objects of the invention may be further achieved in whole or in partby a method of starting the rotation of a rotor of a two-phase switchedreluctance machine (TPSRM) whose main and auxiliary phase windings areenergized under the control of a single controllable current valve.According to this method, current is conducted through the current valvein a single conduction pulse. Then, a determination is made as towhether the TPSRM's rotor is rotating. If not, current is againconducted through the current valve in a single conduction pulse.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be furtherdescribed in the following paragraphs of the specification and may bebetter understood when read in conjunction with the attached drawings,in which:

FIG. 1 illustrates a related art asymmetric power converter for drivinga two-phase SRM;

FIG. 2 illustrates another related art single switch-per-phase powerconverter for driving a two-phase SRM;

FIG. 3 illustrates still another related art C-Dump power converter fordriving a two-phase SRM;

FIG. 4 illustrates still another related art single switch-per-phasepower converter for driving a two-phase SRM;

FIG. 5 illustrates a single-switch power controller in the form of aconverter for driving a two-phase switched reluctance machine (SRM);

FIG. 6 illustrates the four quadrants of torque versus speed operationfor a TPSRM;

FIG. 7( a) illustrates a TPSRM and its flux paths during the excitationof its phase A windings;

FIG. 7( b) illustrates the TPSRM of FIG. 7( a) and its flux paths duringthe excitation of its phase B windings;

FIG. 8 illustrates a rotor and stator of a two-phase SRM motor with mainand auxiliary windings wound on respective stator poles;

FIG. 9 illustrates a drive system for a TPSRM;

FIG. 10 illustrates an algorithm for controlling the drive system,illustrated in FIGS. 9 and 13, while motoring or braking the TPSRMillustrated in FIG. 8;

FIG. 11 illustrates a four-quadrant control algorithm for the drivesystem illustrated by FIG. 9;

FIG. 12 illustrates an algorithm for the operation of the drive systemillustrated in FIG. 9;

FIG. 13 illustrates a block diagram of a system for implementing thespeed control loop and current control loop within the drive systemillustrated in FIG. 9;

FIG. 14 illustrates simulated operational parameters of the drive systemillustrated by FIG. 13; and

FIG. 15 illustrates the measured experimental results corresponding tothe simulation results illustrated in FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 5 illustrates a single-switch power controller in the form of apower converter 500 for driving a two-phase switched reluctance machine(SRM). One winding of the SRM is alternatively referred to as a main orphase A winding 508, while the other winding is referred to as anauxiliary or phase B winding 505. Although phase windings 505, 508 ofthe SRM may be spatially separated from power converter 500 and may alsobe considered to form a part of the machine (also referred to herein asa motor) rather than part of the power converter, these windings 505,508 are illustrated in the power converter circuit for the purpose ofsimplifying the description of their cooperative functionality withpower converter 500.

When power converter 500 is activated by the application of analternating current (ac) source voltage 501, a dc source 510 comes intoeffect through the rectification and filtering provided by a diode 502and a dc source capacitor 503, respectively. As dc source 510 comes intoeffect, current begins flowing through electrical paths that areparallel to capacitor 503. These parallel paths are provided by: (1)auxiliary phase B winding 505 and an auxiliary capacitor 506, providedthat an optional diode 504 is not included in the circuit, and (2) mainphase A winding 508, a diode 507, and auxiliary capacitor 506. The flowof current through these parallel paths charges auxiliary capacitor 506,and the energy stored in auxiliary capacitor 506 generates a current inauxiliary phase B winding 505 and dc source capacitor 503.

Because of the current flow in auxiliary winding 505, there will be apositive or negative torque produced in the SRM, depending on the SRM'srotor position with respect to auxiliary phase B winding 505's statorpoles. If the rotor poles are coming toward the stator poles, theinductance slope is positive, and if the rotor poles are moving awayfrom the stator poles, the inductance slope is negative. If there is anegative inductance slope, the torque produced will be negative and themachine will be generating and sending energy to source capacitor 503.If the inductance slope is positive, auxiliary phase B winding 505 willproduce positive or motoring torque, which is torque output by the SRM.

When the current in auxiliary phase B winding 505 is constant and flowscontinuously, the average torque produced by auxiliary winding 505 iszero. However, current flow through auxiliary winding 505 will notremain constant. After a period of conduction, the current in auxiliarywinding 505 discontinues, and this occurs when the voltages acrossauxiliary capacitor 506 and dc source capacitor 503 equalize.Thereafter, another way must be provided to charge auxiliary capacitor506. A transistor switch 509 provides this other way.

Transistor switch 509 is turned on to provide power to main winding 508.In response to turning on transistor switch 509, a current path isestablished through do source 510, main winding 508, and transistorswitch 509. During the period transistor switch 509 is turned on, mainwinding 508 is operating in its energization mode. Transistor switch 509is turned off either to regulate the current through main winding 508 orto stop its flow completely.

Due to the inductive nature of main winding 508, it is important toprovide a path for the current to flow away from main winding 508 whentransistor switch 509 is turned off. This path is provided by diode 507,auxiliary capacitor 506, do source capacitor 503, and main winding 508itself. The current flowing out of main winding 508 charges auxiliarycapacitor 506, and this flow of current is the predominant way in whichauxiliary capacitor 506 receives a charge, when operating the SRM.

The energy flow in auxiliary capacitor 506 and, hence, in auxiliarywinding 505 is dependent on main winding 508's energy flow and,therefore, its duty cycle. As the speed of the SRM increases, thecontrollable duty cycle of transistor switch 509 increases, therebyincreasing the duration of the voltage applied to main winding 508.Therefore, less charging of auxiliary capacitor 506 occurs, and, hence,less power is provided to auxiliary winding 505. During times ofoperating transistor switch 509 with a high duty cycle, the SRM behavesas though it is a single-phase SRM, with auxiliary winding 505 servingas a window to find the rotor position of the machine through itsinductance. Auxiliary winding 505's inductance can be obtained from itscurrent and voltage waveform or by some other technique known to thoseskilled in the art.

Auxiliary winding 505 returns to dc source capacitor 503 the energy itreceives from main winding 508, when transistor switch 509 is turnedoff. During low speed operation, transistor 509's duty cycle is low andboth auxiliary winding 505 and main winding 508 are active and producemotive power. Therefore, the SRM serves as a two-phase SRM. Thisresembles a capacitor-start and capacitor-run single-phase inductionmotor. It should be noted that such a single-phase induction motor hastwo phase windings.

FIG. 6 illustrates the four quadrants of torque versus speed operationfor a TPSRM. Quadrants I, II, III, and IV correspond respectively to theoperational modes of forward motoring (M), reverse regeneration (RR),reverse motoring (RM), and forward regeneration (FR).

Speed control is achieved in the clockwise (CW) direction of rotation byforward motoring and in the counter-clockwise (CCW) direction ofrotation by reverse motoring. During forward and reverse motoringoperation, the TPSRM produces mechanical power from the input ofelectrical power.

Also, speed control may be achieved when operating the TPSRM as agenerator, during the transition from CW rotation to CCW rotationdirection or vice versa. This operational mode provides the effect of anelectric brake in that mechanical energy is recovered from the storedenergy in the machine's inertia and its load inertia for conversion toelectrical energy. By recovering the mechanical energy, the machine maybe quickly slowed down without the use of a mechanical brake (use of amechanical brake dissipates the energy resulting in low efficiency).When the mechanical energy is not recovered for conversion to electricalenergy, the machine rotation will slow down by its inertia alone, butthis may take longer since the mechanical energy is not harvested.

The transition from forward to reverse motoring is known as forwardregeneration, and the reverse transition is known as reverseregeneration. A more complete description of an SRM's operational modesmay be found in each of “Switched Reluctance Motor Drives”, R. Krishnan,CRC Press, June 2001, and “A Sensorless Switched Reluctance Drive,”Electric Machines and Drives, C E B Green and J M Stephenson, 1997, pp.64-68.

FIG. 8 illustrates a rotor and stator of a two-phase SRM motor with mainand auxiliary windings wound on respective stator poles. Referring toFIG. 8, a two-phase SRM motor 800 is shown having a rotor 801 and astator 803. Rotor 801 has two salient poles 802, and stator 803 has foursalient poles 804, 805. Stator poles 805 have auxiliary winding 505wound around them, and stator poles 804 have main winding 508 woundaround them.

Power converter 500 provides a single-controllable-switch converter tocontrol the speed of TPSRM 800 in all four quadrants of torque versusspeed operation. Two issues related to controlling the four-quadrantoperation of TPSRM 800 with power converter 500 are discussed below.

A first issue concerns starting the rotation of the TPSRM's rotor bothfor instances where the main stator poles are in alignment with therotor poles and not. Though the invention is not limited to anembodiment in which the main and auxiliary windings are equal in numberor size, assume for the purpose of explaining this operational issuethat TPSRM 800 is used. Main winding 508 primarily produces the motivepower and auxiliary winding 505 is used for start-up and for reversingthe rotational direction of the motor.

When rotor poles 802 are aligned with stator poles 804 and main phasewinding 508 is excited, the machine will not produce any torque sincethe rate of change of inductance is zero in this position. An SRMproduces torque only when there is a change of inductance with respectto rotor position. But it is not possible to excite auxiliary phasewinding 505 independently when TPSRM 800 is operated with asingle-controllable-switch converter. Therefore, the rotor and statorpoles must be moved away from an aligned position at the time ofstarting.

Power converter 500 may be used to move the rotor and stator poles awayfrom an aligned position in the following way. Transistor switch 509 ispulsed on for a considerable period of time, and if the machine does notstart, then a second pulse is applied after about one second to make therotor move. No further pulses are needed to start the movement of TPSRM800's rotor.

The second issue concerns, assuming that the machine is reliablystarted, keeping the machine running in quadrants I, II, III and IV inlight of the fact that there is no independent way to energize the main508 and auxiliary 505 phases of TPSRM 800 with power converter 500,since it has only one controllable switch 509. This issue is discussedmore fully below.

A large amount of literature exists concerning the four-quadrant controlof SRM drives, such as described by R. Krishnan, “Switched reluctancemotor drives”, CRC Press, June 2001; Syed Hossain, Iqbal Husain, HaraldKlode, Bruno Lequesne, and Avoki Omekanda, “Four-Quadrant Control of aSwitched Reluctance Motor for a Highly Dynamic Actuator Load”, APEC,2002, pp. 41-47; C E B Green and J M Stephenson, “A Sensorless SwitchedReluctance Drive”, Electric Machines and Drives, 1997, pp. 64-68; B.Fahimi and Raymond B Sepe Jr., “Development of 4-Quadrant SensorlessControl of SRM Drives Over the Entire Speed Range”, IEEE-IAS, 2002, pp.1625-1632; and G. Suresh, B. Fahimi, K. M. Rahman, M. Ehsani, and I.Panahi, “Four-quadrant Sensorless SPM Drive with High Accuracy at AllSpeeds”, APEC, 1999, pp. 1226-1231. However, no literature is known toexist for SRM drives having a single-controllable-switch powerconverter, excluding applicant's patent applications. This is due to theabsence of such a power converter in the related art. Significantfeatures peculiar to this converter are its limited degree ofdirect-current control of a TPSRM's main phase and its heavy dependenceon the auxiliary phase winding and auxiliary capacitor state.Additionally, the degree of control that may be exerted over the currentflowing through the auxiliary winding is dependent on the duty cycle ofthe controllable switch, motor speed and load, and state of theauxiliary capacitor. These constraints on the current control throughthe auxiliary winding have to be-managed very tightly to implementfour-quadrant variable-speed operation of a TPSRM, as described below.

Once TPSRM 800 is started up, the normal running control involvesturning on transistor switch 509 when rotor poles 802 are unaligned withrespect to the main stator poles 804 (i.e., the rotor poles are morenearly aligned with the auxiliary stator poles) and turning W offtransistor switch 509 just before or at the complete alignment of themain stator and rotor poles 804 and 802, respectively. The runningcontrol is described more fully below with respect to the fourspeed-versus-torque operational modes.

Assume the intended direction of rotation for rotor 801 is clockwise(CW). Main winding 508 on main stator poles 804 is energized with acurrent, and this current is commutated when the rotor and main statorpoles 802, 804 align or are close to alignment. During this energizationperiod, the inductance slope of main winding 508 is positive. Hence, thetorque produced is positive and in the direction of rotor 801'smovement. Assuming that a CW rotation is positive, motor 800 isdelivering positive output power (i.e., motoring torque). In otherwords, when the torque and speed are positive, so too is the poweroutput of motor 800. This condition indicates quadrant one operation.

For quadrant four operation, the torque has to be negative when thespeed is positive. As a result, motor 800 delivers negative power inquadrant four operation. That is, the power is taken from SRM 800 andfed to dc source capacitor 503. This is called regeneration in the CWdirection of rotation. In order to produce negative torque, the currentin main winding 508 is injected when rotor poles 802 move away fromalignment with respect to main stator poles 804.

For quadrant three operation, rotor 801 rotates in the counter-clockwise(CCW) direction and torque is applied in this direction, resulting innegative speed and negative torque and contributing to positive power.Therefore, this is motoring in the reverse direction. Reverse directionmotoring is achieved by energizing main winding 508 when rotor poles 802start to move CCW from a completely unaligned position with respect tomain stator poles 804. The current is commutated in main winding 508when the rotor and main stator poles 802, 804 align or are nearalignment.

Quadrant two operation is very similar to that of quadrant four, but thetorque is positive (CW) and the speed is negative (CCW). Quadrant twooperation, therefore, provides negative output power. This isregeneration in the CCW direction of rotation and is realized byenergizing main winding 508 with a current when rotor poles 802 startmoving CCW away from alignment with main stator poles 804.

FIG. 9 illustrates a drive system 900 for a TPSRM. Drive system 900includes power converter 500, SRM 800, a signal interface module 910,and a digital signal processor (DSP) controller 950. Signal interfacemodule 910 has a current sensor 912 for sensing the current flowingthrough main phase winding 508 (or some signal indicative of thiscurrent) and Hall-effect sensors 914 for detecting two discretepositions, spaced 90° apart, of SRM 800's rotor. A voltage converter 916of signal interface module 910 converts the output signals ofHall-effect sensors 914 before providing the converted signals to ageneral input port 952 and an interrupt component 954 of DSP controller950. A signal indicative of the current sensed by current sensor 912 isfiltered and amplified by a low-pass filter/amplifier 918 and providedto DSP controller 950 through its analog-to-digital converter (ADC) 956.DSP controller 950 estimates the rotational speed of SRM 800's rotorfrom successively sensed rotor position signals provided by interruptcomponent 954.

A self-starting component 958 outputs a start-up signal to a speedcommand component 960 so as to activate a speed command, which consistsof the intended magnitude and direction for SRM 800's rotor. Theoperational mode, corresponding to motoring or braking, of SRM 800 isdetermined by an operational mode component 962 based on the speedcommand. If the mode is determined to be the motoring mode, a summer 964calculates a speed error from the difference between the speed estimatedby DSP controller 950, in speed estimator component 966, and the speedcommand provided by operational mode component 962 via a motoring modecomponent 968. The speed error is provided to a speed control loopcomponent 970, which may be a proportional plus integral (PI)controller. Speed control loop component 970 produces a current commandthat is regulated by a current feedback control component, which mayalso be a proportional plus integral type controller.

The current feedback control component comprises a summer 972, a summer974, and a current control loop component 976. Summer 972 determines thedifference between the current command and a digital representation ofthe current signal provided to ADC 956. The difference value output bysummer 972 is provided to current control loop component 976 to producea control signal that is proportional to the duty cycle of transistorswitch 509 in power converter 500. This control signal is provided to apulse width modulator (PWM) 982 and updated for every carrier period ofpulse width modulation control exerted on SRM 800. PWM 982 generates apulse width modulation signal, from the control signal, that is providedto a gate control signal component 920 of signal interface module 910.Gate control signal component 920 produces a gate control signal thatturns transistor switch 509 of power converter 500 on and off.

If the speed command produced by speed command component 960 indicatesthat regenerative braking is to be performed, then DSP controller 950produces the control signal in a different way. Operation mode component962 indicates to a braking mode component 978 that the regenerativebraking mode is in effect. Braking mode component 978 provides anindication of SPM 800's rotor speed to a low speed component 980. If SRM800's rotor speed is above a threshold low speed, summer 974 determinesa difference between a current command that is output by low speedcomponent 980 and the digital representation of the sensed currentsignal output by ADC 956. The difference signal determined by summer 974is provided to current control loop 976 to generate the control signalfor the braking mode of operation, which controls pulse width modulator982 so as to regulate transistor switch 509. If SRM 800's rotor speed islower than the threshold low speed, then low speed component 980provides a reversal pulse to PWM 982 that overrides the control signaloutput by current control loop 976 so that this reversal pulse regulatesthe pulse width modulated signal produced by PWM 982.

Once SRM 800's rotor speed is reversed, the controller automaticallygoes into motoring mode in the opposite direction and current controlloop 976, again, dynamically determines and controls the pulse widthmodulation signal that serves as the gate control signal for transistorswitch 509.

FIG. 10 illustrates an algorithm for controlling the drive system,illustrated in FIGS. 9 and 13, while motoring or braking the TPSRMillustrated in FIG. 8. Operational control of SRM 800 begins with theexecution by self-starting component 958 of a self-starting operation1002 that sets SRM 800's rotor in rotational motion. After self-startingoperation 1002 is complete, operation mode component 962 determines 1004whether the motoring mode is in effect. If so, then monitoring modecomponent 968 regulates 1006 the generation of the current command byspeed control loop component 970. Otherwise, braking mode component 978regulates 1008 the generation of the current command. In either case,current control loop component 976 regulates 1010 the pulse widthmodulation signal generated by PWM 982 based on the current command andthe control signal generated therefrom.

FIG. 11 illustrates a four-quadrant control algorithm for the drivesystem illustrated by FIG. 9. According to this control implementation,drive system 900 continuously monitors the operation of SRM 800 todetermine 1102 whether SRM 800's rotor should change its direction ofrotation. When a change of direction is indicated, a braking sequence isexecuted 1104 to slow the rotational speed of SRM 800's rotor. If theturning speed of SRM 800's rotor is below a threshold speed 1106, then adetermination 1108 of the alignment between SRM 800's rotor and statorpoles is made. Otherwise, the braking sequence 1104 is continued. If SRM800's rotor and stator poles are unaligned, then the pulse widthmodulation signal applied to transistor switch 509 is discontinued 1110.Otherwise, drive system 900 waits until SRM 800's rotor and stator poleshave rotated to an unaligned position. After the pulse width modulationsignal is discontinued 1110, drive system 900 executes a delay operation1112, for a particular period of time, before generating a reversalstart pulse 1114. Thereafter, the pulse width modulation signal isreactivated 1116 so that a motoring sequence 1118 may be executed forcontrolling SRM 800's rotor.

Accordingly, a purpose of the four-quadrant control algorithm is to setup a PWM sequence with respect to a quadrant command and to generate astart pulse for reversal. After the rotor speed reaches the desiredspeed, the starting signal for reversal will be applied to the powerconverter.

DSP controller 950 checks 1108 for an unaligned position of SRM 800'srotor and stator poles, in the four-quadrant control algorithmillustrated in FIG. 11, so as to obtain a huge negative torque withshort delay. The maximum negative torque can be produced after the rotorpasses the unaligned position (90°) (i.e., preferably more than half waybetween adjacent stator poles in its rotation). PWM off 1110 indicatesthe deactivation of the PWM function, so as to slow and decrease thecurrent flow in main winding 508. Delay 1112 is the time duration neededto move rotor 801 to the maximum negative torque position.

FIG. 12 illustrates an algorithm for the operation of drive system 900.According to this algorithm, DSP controller 950 initializes 1202 itsmode of operation by examining SRM 700's rotor position and the sensedcurrent provided by Hall-effect sensors 914. Additionally, DSPcontroller 950 determines its operational command parameters andinitializes a timer, ADC 956, general input port 952, interruptcomponent 954, its external interrupt functions, and its operatingvariables. After initialization, DSP controller 950 applies 1204 asingle pulse to transistor switch 509 via signal interface module 910.If this pulse does not cause SRM 800's rotor to begin turning, asdetermined in step 1206, another pulse is applied 1204. If rotor 901 isdetermined 1206 to be turning DSP controller 950 determines 1208 therotor's direction of rotation, sets 1208 a speed command, such as 5000revolutions per minute (rpm), and sets 1208 SRM 800's operational modeto the motoring mode. Thereafter, DSP controller 950 drives 1210 thesingle switch SRM (SSSR) 800's motoring operation in accordance with aproportional integrator (PI) speed control loop and a PI current controlloop, until the speed command is determined 1212 to have changed. Whenthe speed command is changed to indicate a reversal of rotationaldirection for SSSRM 800's rotor, DSP controller 950 drives 1214 abraking operation for SSSRM 800 using a PI current control loop, untilthe rotational speed of SSSRM 800's rotor is determined 1216 to berotating at less than a threshold speed, such as 250 rpm. When therotor's speed falls below this threshold, DSP controller 950 deactivates1218 the PWM control of transistor switch 509 and waits 1218 anestablished delay time before applying 1218 a reversal pulse to SSSRM800's rotor. Then, DSP controller 950 establishes 1220 this reversedirection of rotation as the desired direction and re-establishes themotoring operation drive 1210 for the new direction of the rotor'srotation.

FIG. 13 illustrates a block diagram of a system for implementing thespeed control loop and current control loop within the drive systemillustrated in FIG. 9. A summer 1302 determines a speed error signal bysubtracting a filtered speed indication signal from a speed command.This speed error signal is provided to a speed controller and limiter1306, which generally is a proportional plus integral type controller.Speed controller and limiter 1306 performs a predetermined operation onthe speed error signal and outputs the result to a current commandcontroller 1308. Current command controller 1308 performs apredetermined operation on the signal provided by speed controller andlimiter 1306 to generate a current command.

The current command can be determined in many ways. The standard methodis to set the current command proportional to the square root of atorque command, which is the output of the speed controller and limiter1306. The present invention is not restricted by the algorithm that maybe used in the current command generator.

A summer 1310 determines a current error signal by subtracting afiltered indicator of the current flowing through transistor switch 509from the current command. Current controller 1314 performs apredetermined operation on the current error signal and outputs theresult to a PWM controller 1316. PWM controller 1316 generates a pulsewidth modulation signal from the signal received from current controller1316. The pulse width modulation signal is provided to power converter500 for turning on and off transistor switch 509 and thereby controllingthe energization of SRM 800's phase windings. A current filter 1312filters, using a low pass filter, the sensed indicator of the currentflowing between power converter 500 and SRM 800, and a filter 1304filters the rotor speed obtained from processing the rotor positionsignals, sensed from SRM 800, in a DSP or from a hardware circuit.

FIG. 14 illustrates simulated operational parameters of the drive systemillustrated by FIG. 13. Torque and current parameters are graphed as afunction of an applied speed command for the four-quadrant operationalmodes of forward motoring, forward regeneration, reverse motoring, andreverse regeneration. The units of measure for the parametersillustrated in FIG. 14 are presented in normalized units (e.g., 1 p.u.means 100%. times the base value of the variable).

As may be seen in FIG. 14, when the rotor speed and its command arepositive, then SRM 800 is in its quadrant I mode of operation of forwardmotoring. Note that during this time, the power is positive as themachine is being powered by the positive torque to keep it running inthe CW direction (by the convention used herein, CW speed is positivespeed).

When the command speed is made negative so as to make SRM 800 run in thenegative direction (CCW), the torque of the machine is made negative.Hence, the power output is negative, indicating that the machine isoperating as a generator by transferring mechanical energy from themachine to the power supply as electrical energy. This brakes themachine rotor resulting in a faster decrease in speed. The speed ispositive (CW) but torque is negative. Therefore, SRM 800 is in itsquadrant IV mode of operation of forward regeneration.

When the machine rotor reaches zero speed, the machine continues toproduce negative torque, thus causing the motor rotor to rotate in theCCW direction (because positive torque runs the rotor in the CWdirection), which is negative speed (as CW speed is positive). Thiscorresponds to the quadrant III mode of operation, as the speed andtorque are both negative and the resulting power is positive. That is,the machine produces mechanical power while taking in electrical power(same as in quadrant I). Therefore, this operational mode is reversemotoring.

When the speed command is made to go from negative speed to say zerospeed, while SRM 800 is operating in the quadrant III mode of operation,the machine is slowed down by applying a torque that is opposite to whatwas previously being applied (that is negative). Therefore, a positivetorque has to be generated and applied. The torque command goes fromnegative to positive and the torque becomes positive as soon as thespeed is commanded. The torque is positive and the speed is negative atthis time, thus producing negative power. That is, the output power iselectrical and the input power is mechanical power resulting in theslowing down of the machine. This is the quadrant II operational mode ofreverse regeneration.

FIG. 15 illustrates the measured experimental results corresponding tothe simulation results illustrated in FIG. 14. The units of measure forthe graphed rotor speed and its command are 5,000 rpm/division, the unitof measure for the current is 10A/division, and the unit of measure forthe time is 5s/division. As may be determined by comparison of FIGS. 14and 15, the simulation results correspond closely to the experimentalresults.

The foregoing description illustrates and describes the presentinvention. However, the disclosure shows and describes only thepreferred embodiments of the invention, but it is to be understood thatthe invention is capable of use in various other combinations,modifications, and environments. Also, the invention is capable ofchange or modification, within the scope of the inventive concept, asexpressed herein, that is commensurate with the above teachings and theskill or knowledge of one skilled in the relevant art.

The embodiments described herein are further intended to explain bestmodes known of practicing the invention and to enable others skilled inthe art to utilize the invention in these and other embodiments, withthe various modifications that may be required by the particularapplications or uses of the invention. Accordingly, the description isnot intended to limit the invention to the form disclosed herein.

1. A method of regulating the speed of a two-phase switched reluctancemachine (TPSRM) rotor, the method comprising: selecting either amotoring mode or a braking mode of operation for the TPSRM; regulatingthe rotor speed, when the motoring mode is selected, using a controlsignal cooperatively produced by a speed control feedback loop and acurrent control feedback loop; and regulating the rotor speed, when thebraking mode is selected, using a control signal produced by the currentcontrol feedback loop without the cooperation of the speed controlfeedback loop, wherein: the speed control feedback loop uses anestablished speed control signal and a signal indicative of the rotor'sspeed to dynamically adjust a first parameter governing the controlsignal, the current control feedback loop uses an established currentcontrol signal and a signal indicative of the current flowing through astator winding of the TPSRM to dynamically adjust a second parametergoverning the control signal, and the braking mode of operation convertsthe TPSRM's mechanical energy into electrical energy to produce abraking effect on the rotation of the rotor.
 2. The method of claim 1wherein the established current control signal is determined inaccordance with the value of the first parameter when the motoring modeis selected.
 3. The method of claim 1 further comprising modulatingcurrent conduction through a single controllable current valve using thecontrol signal to vary the energy applied to or drawn from the TPSRMrotor.
 4. The method of claim 3 further comprising: modulating thecurrent conduction through the single controllable current valve tooperate the TPSRM in a forward motoring mode of operation; andmodulating the current conduction through the single controllablecurrent valve to operate the TPSRM in a forward regeneration mode ofoperation.
 5. The method of claim 3 further comprising: modulating thecurrent conduction through the single controllable current valve tooperate the TPSRM in a reverse motoring mode of operation; andmodulating the current conduction through the single controllablecurrent valve to operate the TPSRM in a reverse regeneration mode ofoperation.
 6. The method of claim 4 further comprising: modulating thecurrent conduction through the single controllable current valve tooperate the TPSRM in a reverse motoring mode of operation; andmodulating the current conduction through the single controllablecurrent valve to operate the TPSRM in a reverse regeneration mode ofoperation.
 7. A drive system for regulating the speed of a two-phaseswitched reluctance machine (TPSRM) rotor, the system comprising: aspeed control feedback loop component that uses an established speedcontrol signal and a signal indicative of the rotor's speed todynamically adjust a first parameter; and a current control feedbackloop component that uses an established current control signal and asignal indicative of the current flowing through a stator winding of theTPSRM to dynamically adjust a second parameter, wherein: a controlsignal for regulating the speed of the TPSRM rotor is produced inaccordance with the first and second parameters when the TPSRM isoperated in a motoring mode, the control signal for regulating the speedof the TPSRM rotor is produced in accordance with the second parameterbut not the first parameter when the TPSRM is operated in a brakingmode, and the braking mode of operation converts the TPSRM's mechanicalenergy into electrical energy to produce a braking effect on therotation of the rotor.
 8. The system of claim 7 wherein the establishedcurrent control signal is determined in accordance with the value of thefirst parameter when the TPSRM is operated in the motoring mode.
 9. Thesystem of claim 7 further comprising a single controllable current valvewhose current conduction is modulated using the control signal so as tovary the energy applied to or drawn from the TPSRM rotor.
 10. The systemof claim 9 wherein the established speed and current control commandsignals determine whether the control signal causes the TPSRM to operatein a forward motoring mode of operation or a forward regeneration modeof operation.
 11. The system of claim 9 wherein the established speedand current control command signals determine whether the control signalcauses the TPSRM to operate in a reverse motoring mode of operation or areverse regeneration mode of operation.
 12. The system of claim 10wherein the established speed and current control command signals alsodetermine whether the control signal causes the TPSRM to operate in areverse motoring mode of operation or a reverse regeneration mode ofoperation.
 13. A method of reversing the rotational direction of atwo-phase switched reluctance machine (TPSRM) rotor, the methodcomprising: regulating the flow of current through a single controllablecurrent valve to maintain a forward motoring mode of operation for theTPSRM; regulating the flow of current through the single controllablecurrent valve to cause the TPSRM's mechanical energy to be convertedinto electrical energy so as to produce a braking effect on the rotationof the rotor; interrupting the flow of current through the singlecontrollable current valve for a period of time; and regulating the flowof current through the single controllable current valve, after theperiod of time has expired, to induce the TPSRM's rotor to reverse itsdirection of rotation.
 14. The method of claim 13 further comprising:determining the position of the TPSRM's rotor poles with respect to theTPSRM's stator poles; and determining the period of time forinterrupting the flow of current through the single controllable currentvalve in accordance with the determined position of the rotor poles. 15.The method of claim 14, wherein the flow of current through the singlecontrollable current valve remains interrupted until the rotor poles areexpected to have rotated more than half way between adjacent statorpoles.
 16. The method of claim 14, wherein the period of time duringwhich the flow of current through the single controllable current valveis interrupted is no less than the period of time expected for the rotorpoles to have rotated more than half way between adjacent stator poles.17. A system for reversing the rotational direction of a two-phaseswitched reluctance machine (TPSRM) rotor, the system comprising: acontroller; and a single controllable current valve that regulates,under the control of the controller, the current flowing through thecurrent valve so as to establish the rotational direction and speed ofthe rotor, wherein: the controller and the current valve cooperate tomaintain a forward motoring mode of operation for the TPSRM, when theTPSRM's rotor is to continue rotating in its current direction, thecontroller and the current valve cooperate to cause the TPSRM'smechanical energy to be converted into electrical energy so as toproduce a braking effect on the rotation of the rotor, when a reversalin the rotor's direction of rotation is to be achieved, the controllerand the current valve cooperate to interrupt the flow of current throughthe single controllable current valve for a period of time, after therotor speed has been reduced by the braking effect, and the controllerand the current valve cooperate to regulate the flow of current throughthe single controllable current valve, after the period of time hasexpired, to induce the TPSRM's rotor to reverse its direction ofrotation.
 18. The system of claim 17, wherein: the controller determinesthe position of the TPSRM's rotor poles with respect to the TPSRM'sstator poles; and the controller determines the period of time forinterrupting the flow of current through the single controllable currentvalve in accordance with the determined position of the rotor poles. 19.The system of claim 18, wherein the flow of current through the singlecontrollable current valve remains interrupted until the rotor poles areexpected to have rotated more than half way between adjacent statorpoles.
 20. The system of claim 18, wherein the period of time duringwhich the flow of current through the single controllable current valveis interrupted is no less than the period of time expected for the rotorpoles to have rotated more than half way between adjacent stator poles.21. A method of starting the rotation of a rotor of a two-phase switchedreluctance machine (TPSRM) whose main and auxiliary phase windings areenergized under the control of a single controllable current valve, themethod comprising: conducting current through the current valve in asingle conduction pulse; determining whether the TPSRM's rotor isrotating; and conducting current through the current valve in a singleconduction pulse again, if the rotor is determined not to be rotating.